Cell migration is an essential process in multicellular organisms, gaining great importance during embryogenesis and in the immune response. To migrate the cells must be able to generate protrusions outside the cell margin. The main types of actin protrusions are lamellipodia and filopodia, both generated by actin polymerization through the Arp2/3 (Actin related protein) complex. It has been reported that the activation of numerous small GTPases complex including Rab35, which recruits Rac1 and Cdc42 to the site of protrusions formation, where the latter are involved in the formation of lamellipodia and filopodia respectively.
p53-related protein kinase (PRPK) is a highly conserved atypical kinase. It is a member of the KEOPS (kinase, putative endopeptidase and other proteins of small size) complex, which modulates the efficiency of recognition of ANN codons. In Drosophila PRPK is necessary for the translation of PI3K/TOR growth signals, which lastly support cell growth and proliferation. However, we observed that loss of function of PRPK alters cellular shape in haemocytes -macrophage-like cells-, generating a star-like phenotype which is also observed in loss of function of the Arp2/3 complex. The phenotype is suppressed by co-expressing Rab35. Also, it has been reported physical interaction between PRPK and Rab35 in human cells.
With all this evidence I decided to determine if PRPK has a function independent of the KEOPS complex participating in the dynamics of membrane protrusions and migration pattern of haemocytes in Drosophila melanogaster. To do this, we manipulated PRPK levels in tissues and times specific through the Gal4 / UAS system. In particular contexts, migration and cell cultures, the actin cytoskeleton dynamics and cell migration's parameters were analyzed by confocal microscopy. Finally co-immunoprecipitations were performed to determine the physical interaction between PRPK-kae1 (another member of the complex KEOPS) and PRPK-Rab35.
The results obtained in this study show that the loss of function of PRPK alters the dynamics of membrane protrusions in vitro and the migration pattern of embryonic haemocytes, reduces the recruitment of larval haemocytes in response to tissue damage and decreases haemocyte migration rate in pupal stage. We confirmed the physical interaction between PRPK and Rab35 and even when PRPK interacts with kae1, it was concluded that the role of PRPK in determining cell shape is due to a non-canonical role independent of the KEOPS complex. These results suggest that PRPK has two roles: Integration of growth signals and cell migration